Conventional continuous tube rolling mills are extremely complex installations requiring large capital investments that can only be paid back if high capacities are well utilized. There is a rising demand world-wide, however, for smaller capacity plants with a correspondingly lower investment burden. This is particularly true in the specialty pipe business, where manufacturing specialty pipe from long hollow tubes may be cost prohibitive.
Specialty pipe (or tubing) refers to a wide variety of high-quality, custom-made tubular products requiring critical tolerances, precise dimensional control and special metallurgical properties. Specialty pipe is typically used in the manufacture of automotive, construction and agricultural equipment, oil country tubular good (OCTG) applications, petrochemical applications, and industrial applications such as hydraulic cylinders, machine parts and printing rollers. OCTG is a label typically applied to the pipe products used by petroleum exploration and production customers, such as tubing, casing, pup joints, risers and couplings.
In order to produce specialty pipe that meets more stringent standards, pipe produced from traditional methods, such as electric resistant welding (ERW) technology, is then worked to form specialty pipe with more exacting qualities. Often, specialty pipe needs to be sized in order to meet customer standards. Typical methods to decrease an outer diameter of a pipe involve using rollers or drawing through a die. Using rollers typically is disadvantageous because roller systems often cannot produce pipe with tight tolerances. Many specialty pipes, such as stabilizer bars in the automotive industry, require precise tolerances of 9/1000's of an inch.
Other methods of sizing pipe, such as drawing through a die, may produce pipes with tight tolerances. However, drawing systems have disadvantages as well. Drawing a pipe through a die typically requires auxiliary pre-treatment and post-treatment operations. For example, required pre-treatment operations include pickling and lubricating the pipe as well as swaging one end of the pipe (thereby creating about a 12% material loss). Drawn pipes also typically require post-treatment operations to straighten and stress relieve the tube. Stress relieving is often necessary because typical drawing systems use mandrels that cause the pipe to lose a significant portion of the pipe's fracture toughness when drawn through an associated die.